Catalytic cracking apparatus using cross-flow regenerator

ABSTRACT

An process and apparatus are disclosed for fluidized bed catalyst regeneration in a cross-flow type regenerator. A baffled coked catalyst inlet located within the dense bed of catalyst disperses and distributes coked catalyst flow in a direction generally normal to the direction of flow in the catalyst inlet. The baffle significantly reduces the stagnant regions in the bed.

This application is a continuation of abandoned application Ser. No.571,399 filed Aug. 23, 1990, which is a division of application Ser. No.431,953 filed Nov. 6, 1989 and now U.S. Pat. No. 4,980,048 issued Dec.25, 1990.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the regeneration of fluidized catalyticcracking catalyst.

2. Description of Related Art

Catalytic cracking of hydrocarbons is carried out in the absence ofexternally supplied H2, in contrast to hydrocracking, in which H2 isadded during the cracking step. An inventory of particulate catalyst iscontinuously cycled between a cracking reactor and a catalystregenerator. In the fluidized catalytic cracking (FCC) process,hydrocarbon feed contacts catalyst in a reactor at 425 C.-600 C.,usually 460 C.-560 C. The hydrocarbons crack, and deposit carbonaceoushydrocarbons or coke on the catalyst. The cracked products are separatedfrom the coked catalyst. The coked catalyst is stripped of volatiles,usually with steam, and is then regenerated. In the catalystregenerator, the coke is burned from the catalyst with oxygen containinggas, usually air. Coke burns off, restoring catalyst activity andsimultaneously heating the catalyst to, e.g., 500 C.-900 C., usually 600C.-750 C. Flue gas formed by burning coke in the regenerator may betreated for removal of particulates and for conversion of carbonmonoxide, after which the flue gas is normally discharged into theatmosphere.

Most older FCC units regenerate the spent catalyst in a single densephase fluidized bed of catalyst. The single dense bed usually flows ineither a swirl pattern, or in a crossflow pattern. These units work, butat relatively low efficiency compared to more modern designs. The olderunits have had problems in establishing a desired gas flow through thebed, or were considered inefficient because they maintained the catalystas a "bubbling" dense phase fluidized bed. Bubbling dense beds havenever worked as well in large refinery units as they do in pilot plantsize units. Much of the deficiency in operation was laid to the presenceof large bubbles in the bed, which meant that the dense phase fluidizedbed was not being efficiently used much of the time.

Most new units are of the High Efficiency Regenerator (H.E.R.) designusing a coke combustor, a dilute phase transport riser, and a seconddense bed, with recycle of some hot, regenerated catalyst from thesecond dense bed to the coke combustor. Units of this type are shown inU.S. Pat. No. 3,926,778 (which is incorporated by reference) and manyother recent patents. The H.E.R. design is used in most new unitsbecause it permits operation of an FCC with less catalyst inventor (andhence less catalyst loss), and because such units tend to have both lessCO emissions and less NOx emissions than the single dense bedregenerators.

The high efficiency design uses a fast fluidized dense bed for cokecombustion. These dense bed are intensely agitated, and large bubblesare not stable in such beds. The high efficiency regenerator design canachieve complete regeneration of catalyst with perhaps half the catalystinventory required in the older regenerators, using a bubbling fluidizedbed.

In FCC units, much of the catalyst is lost due to attrition, and anincrease in catalyst inventory increases catalyst loss to attrition.Much of the activity loss of the FCC catalyst is due to steaming in theregenerator. This steaming is not intentional, but most regeneratorsoperate with 5-10 psia steam partial pressure (due to entrainedstripping steam, and water of combustion). Thus the regenerator is notonly a regenerator, it is a catalyst steamer, and deactivator. Increasedcatalyst inventory in the regenerator leads to increased steaming anddeactivation of the FCC catalyst.

There is therefore a great incentive to do everything possible to reducethe catalyst inventory of a regenerator, and to improve the efficiencyof the regenerator. That is why a majority of new FCC construction usesthe high efficiency regenerator design.

Unfortunately, it has not been economically justifiable to convert olderstyle, single dense bed regenerators to the modern H.E.R. design becauseof the high capital cost associated with simple scrapping of the oldsingle bed regenerator. Attempts to simply use the old single stageregenerator as part of a modern two stage, H.E.R. design have not beentoo successful, as the old single stage units are much larger thaneither of the beds in an H.E.R. unit. Another complication has been thatmany of the older units were not designed to operate at the highertemperatures associated with complete CO combustion.

Rather than scrap older FCC regenerators, refiners have tried to improvethem, and the FCC process, as much as possible with improvements incatalyst and catalyst additives.

Actually, refiners have known for many years that there were problemswith bubbling bed regenerators. Problems exist in both cross-flowregenerators and in swirl type regenerators, however more has beenpublished on problems in swirl units, so these will be reviewed first.

A typical swirl type regenerator is shown in U.S. Pat. No. 3,817,280,which is incorporated herein by reference.

The swirl type regenerator adds spent catalyst to an FCC regeneratorhaving a generally circular cross section. The catalyst is added via asingle inlet, to the dense bed of catalyst in the regenerator in atangential direction, imparting a swirling motion to the dense bed. Thecatalyst swirls around roughly 3/4 of the regenerator, and then iswithdrawn as regenerated catalyst for reuse in the FCC process.

The swirl regenerator is an elegant concept which causes problems inpractical operation. The spent catalyst, laden with coke and poorlystripped hydrocarbons, is added to one portion of the bed. The catalystremoved after one radial traverse of the bed has essentially nounstripped hydrocarbons, and a very low level of residual coke or carbonon catalyst. For efficient operation, the amount of regeneration gasadded should roughly equal the amount of combustible substance to beburned, and this means that very large amounts of combustion air areneeded where spent catalyst is added, and almost no combustion air isneeded where catalyst is withdrawn.

FCC operators have provided means for improving the distribution ofcombustion air to such regenerators. In U.S. Pat. No. 3,817,280, abetter way of controlling the distribution of combustion air wasprovided. The air distribution grid beneath the bubbling dense bed wasradially segmented, and means were provided for adjusting the flow ofcombustion air to each radial segment. In this way it was possible tofine tune the amount of air added to different radial segments of thebubbling fluidized bed.

The approach of U.S. Pat. No. 3,817,280 provided a better way todistribute the air to a swirl type regenerator. It ignored the problemof inefficiencies regards the distribution of solids to a swirl typeregenerator.

U.S. Pat. No. 3,904,548, which is incorporated herein by reference,recognized the problem of efficient operation of a large size, fluidizedbed, swirl type regenerator. A baffle was provided, adjacent thetangential catalyst inlet, to mix some regenerated catalyst withincoming stripped catalyst. The baffle provided an expanding annulus ofabout 20 degrees in the direction of catalyst flow, to prevent undesiredcatalyst circulation.

The operation of swirl, cross-flow, and other types of regenerators wassignificantly improved by the use of CO combustion promoters, discussedhereafter.

U.S. Pat. Nos. 4,072,600 and 4,093,535 teach use of combustion-promotingmetals such as Pt, Pd, Ir, Rh, Os, Ru and Re in cracking catalysts inconcentrations of 0.01 to 50 ppm, based on total catalyst inventory.Such combustion promoters improve the rate of CO burning in all types ofregenerators, both modern and old. CO combustion promoters help minimizeCO emissions, but can cause an increase in the amount of nitrogen oxides(NOx) in the regenerator flue gas. It is difficult in a catalystregenerator to completely burn coke and CO in the regenerator withoutincreasing the NOx content of the regenerator flue gas. Swirl typeregenerators are especially troublesome in this regard, i.e., enoughexcess air and CO combustion promoter can be added to meet CO limits,but this will greatly increase NOx emissions Cross-flow regeneratorshave similar problems.

We realized that there was a problem with the basic design of thecross-flow regenerator used in many commercial FCC units. The problemwas not so much with air distribution, but rather with stagnant regionsin the bubbling bed. We studied cross-flow type regenerators, and foundthat in many units 50% or more of the dense bed of catalyst wasrelatively stagnant.

We discovered a way to overcome many of the deficiencies of catalystdistribution in cross-flow type regenerators by making changes in theway that catalyst was distributed after it was added to the dense bed.We found a way to retain the single spent catalyst inlet used in theseunit, and distribute this catalyst internally, after addition ofcatalyst to the dense phase fluidized bed, to reduce greatly thestagnant areas of the dense bed. We found a way to do this withoutaltering the catalyst withdrawal sink.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for the fluidizedcatalytic cracking (FCC) of a hydrocarbon by contact of a crackablehydrocarbon with a source of regenerated FCC catalyst in a crackingreactor to produce catalytically cracked products and coked FCC catalystwhich is regenerated in a cross-flow type regenerator which maintains adense phase, bubbling fluidized bed of catalyst having a depth of atleast 8 feet within a regenerator vessel having a diameter of at least 8feet, and wherein at least 35% of said dense bed is relatively stagnantand said coked cracking catalyst is added via a single coked catalystinlet having an inlet diameter of at least 1 foot and connective withone side of said regenerator, said inlet discharging said coked catalystinto said dense bed, and said coked catalyst is regenerated in saiddense bed by contact with an upflowing supply of oxygen or an oxygencontaining gas to produce regenerated catalyst which is withdrawn fromsaid catalyst bed via a catalyst outlet located in a lower portion ofsaid dense bed, said outlet being on the other side of said dense bedrelative to said inlet whereby there is a general cross-flow of cokedcatalyst from the inlet to the regenerated catalyst outlet,characterized by providing a baffle within said regenerator dense bedwhich is operatively associated with said catalyst inlet to disperse anddistribute incoming spent catalyst into at least two streams of spentcatalyst within said dense bed and to reduce the amount of said densebed which is stagnant, said baffle having a baffle diameter, as measuredon a plane normal to said coked catalyst inlet, at least equal to thediameter of said coked catalyst inlet; a baffle height of at least 8feet; and wherein said baffle is spaced inwardly from an outer wall ofsaid regenerator by a distance at least equal to the diameter of saidcatalyst inlet.

In an apparatus embodiment, the present invention provides an apparatusfor the fluidized catalytic cracking (FCC) of a hydrocarbon by contactof a crackable hydrocarbon with with a source of regenerated FCCcatalyst in a cracking reactor means to produce catalytically crackedproducts and coked FCC catalyst which is regenerated in a cross-flowtype regenerator means to produce regenerated catalyst which is recycledto said cracking reactor means, characterized by a baffled cross-flowtype regenerator means comprising in operative combination: aregenerator vessel having a diameter of at least 8 feet, and adapted tomaintain a dense phase, bubbling fluidized bed of catalyst having adepth of at least 8 feet; a coked FCC catalyst inlet comprising a singlecatalyst inlet having an inlet diameter of at least 1 foot andconnective with a side of said regenerator a regeneration gas inletconnective with an air distribution means in a lower portion of saidregenerator vessel; a flue gas outlet means in an upper portion of saidregenerator vessel for removal of flue gas: a non-centrally locatedregenerated catalyst outlet located in a lower portion of said dense bedand near a side of said regenerator vessel, said outlet being on theother side of said dense bed relative to said spent catalyst inletwhereby there is a general cross-flow of coked catalyst from said cokedFCC catalyst inlet to the regenerated catalyst outlet: and a bafflewithin said regenerator dense bed which is operatively associated withsaid catalyst inlet to disperse and distribute incoming spent catalystinto at least two streams of spent catalyst within said dense bed, saidbaffle having a baffle diameter, as measured on a plane normal to saidcoked catalyst inlet, at least equal to the diameter of said cokedcatalyst inlet; a baffle height of at least 8 feet; and wherein saidbaffle is spaced inwardly from an outer wall of said regenerator by adistance at least equal to 50% of the diameter of said catalyst inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) is a simplified, cross-sectional view of a cross-flowtype regenerator

FIG. 2 (prior art) is a cross sectional view of the regenerator of FIG.1, showing the catalyst flow across the regenerator.

FIG. 3 is a simplified, cross sectional view of an improved regeneratorof the present invention, with a baffled catalyst inlet.

FIG. 4 is a simplified, schematic view of an improved regenerator of thepresent invention, with a baffle mounted on, and supported by, the cokedcatalyst inlet.

FIG. 4A is an elevation view of the FIG. 4 baffle.

DETAILED DESCRIPTION

The invention can be better understood with reference to the drawings,and a discussion of the prior art cross-flow type regenerator.

FIG. 1 (prior art) is a simplified, cross-sectional view of a cross-flowtype regenerator which is typical of many in commercial use.

Spent catalyst in line 4 is discharged down into regenerator 2. Airpasses up into the regenerator via air grid 14, and fluidizes andregenerates the catalyst, which is maintained as a bubbling fluidizeddense phase bed.

Catalyst flows across the regenerator, and is removed via sink 8 whichis in the base of the air grid 14, and is therefore on the bottom of thebubbling fluidized bed of catalyst.

Flue gas and entrained catalyst rise above the bubbling bed, passthrough primary cyclone 31 and secondary cyclone 41. Catalyst isrecycled to the dense bed via diplegs 32 and 42, while flue gas isdischarged via outlet 32.

FIG. 2 shows a typical flow pattern in a cross-flow regenerator such asthat shown in FIG. 1. Much of the spent catalyst tunnels through thedense bed to catalyst sink 8. Much of the dense bed is relativelyinactive.

FIG. 3 shows one preferred embodiment of the present invention, across-flow type regenerator with a baffled catalyst inlet.

FIG. 3 is closely patterned after FIG. 2, and elements 2, 4 and 8 arethe same in each figure. The baffle 100 is essentially the only changebetween FIG. 2 and FIG. 3, but there is a profound change in the flowpatterns, and size of the stagnant regions in the dense bed.

Baffle 100 splits and distributes the incoming spent catalyst, and evenmixes the incoming spent catalyst to a certain extent with theregenerated catalyst already in the dense bed. The flow patterns aremuch improved, as is evident from a comparison of FIG. 3 to FIG. 2.

FIG. 4 shows a baffle supported by the coked catalyst inlet 404 whichextends well into the regenerator vessel through vessel walls 402. Thebaffle 500 is displaced from, and affixed to, the coked catalyst inletpipe 404 via support means 502 and 503. The baffle 500 shown is made upof two rectangular plates 510 and 511. Baffle 500 may also have anyother suitable shape which will split or deflect catalyst flow, such asa square, rectangle or circle comprising a single plate. The baffle mayeven deflect catalyst flow back toward the catalyst inlet, much asthrust reversers on a jet engine can be used to reverse the direction offlow of a fluid.

The diameter A of the coked catalyst inlet is shown superimposed on thebaffle 500, which preferably has a dimension, as measured normal tocatalyst flow in pipe 404, of 2A.

The baffle 500 can be at any desired angle relative to the catalystinlet pipe 404. Baffle 500 can be generally vertical, i.e. parallel tovessel wall 402, in which case it will behave very much like a verticalbaffle affixed to the air grid. Baffle 500 can be generally horizontal,i.e., parallel to the air grid and normal to the wall 402 of theregenerator vessel. The precise angle chosen depends to some extent onthe penetration of pipe 404 into vessel 402, and on the angle at whichcoked catalyst is discharged from pipe 404. In most FCC regenerators thecatalyst will be discharged down into the regenerator vessel, usually atan angle from the horizon (or the surface of the dense bed of catalyst)ranging from 30 to 50 degrees, and preferably at an angle ranging from35 to 45 degrees, roughly as shown in the Figure. For these units, itwill be best to use a baffle which is as shown in the Figure, i.e., onehaving an angle from the horizontal of 10 to 75 degrees. The baffleshould be made of two rectangular plates affixed to define an angle of90 to 150 degrees. The embodiment shown in FIG. 4 allows a significantamount, roughly 20% of the coked catalyst entering the regeneratorvessel, to bypass the baffle, and flow more or less directly into thecatalyst dense bed, over baffle 500.

EXPERIMENTS--COMPUTER SIMULATIONS

Extensive experimental work studying commercial and laboratory sizefluidized bed, and further work on developing a computer program whichallowed us to accurately model the behavior of large, commercial FCCregenerators.

As a result of our study, we discovered that the conventional cross-flowtype regenerator, such as that disclosed in FIG. 1 and FIG. 2, leaves65% of the dense phase, bubbling fluidized bed of catalyst relativelystagnant. We define a stagnant region as one where the predictedstreamlines form a closed loop, i.e., the net flow of catalyst frominlet to outlet is outside the boundaries of this loop. The catalystwithin the loop, or stagnant region, can be well fluidized, but it isnot going anywhere. Thus as used herein, stagnant refers more to activechemical reactions taking place, or efficient coke burning within aregion, rather than the more classical concept of stagnant regions,where there is no flow at all.

We tried to improve this design using multiple inlets. Although someimprovement was noted, there was not enough improvement to justify thecapital cost of splitting the spent catalyst into two or more streams.It costs a lot to split the catalyst flow into two streams because thecatalyst flows are so large (on the order of 2000 to 4000 tons per hourof catalyst). To achieve a good, uniform division of catalyst the pipingused must be mirror image symmetrical or something close to this. Valvescan be used to control catalyst flow, but because of the large size ofthe catalyst flows being contemplated, and the high temperatures, around1000 F., it usually will not be cost effective to use valves to assure a50/50 split of catalyst.

We tried moving the regenerated catalyst withdrawal point from its oldlocation to a central location, and adding catalyst from 2 or moresymmetrical locations. Again, some improvement was noted, but not enoughto justify the substantial costs of splitting the catalyst inlet lineand the further substantial costs of moving the catalyst outlet line.The catalyst outlet line is expensive to move because of the size ofthis line, typically 5 to 8 feet in diameter. There are also substantialcosts associated with cutting into the regenerator vessel at a new placeto accommodate the new outlet line, and plugging of the old outlet.

We were aware of the use of baffles to improve operation of swirl flowtype regenerators. We studied the operation of a swirl type regenerator,and found that the use of anti-bypass baffles either made littleimprovement, or actually made things worse regards stagnant regions ofthe bed. Despite the discouraging results with baffles in swirl typeregenerators, we persisted in studying the use of baffles in cross-flowtype regenerators.

The breakthrough came when we used a baffle in a cross-flow typeregenerator located within the catalyst dense bed to, in effect, splitthe spent catalyst addition in two. By using an inlet baffle in a crossflow regenerator, we were able to significantly increase the activearea, or non-stagnant area, of the bed.

The results of the computer simulation are reported below in the table.Simulation 1 represents a conventional, prior art, cross flowregenerator design.

    ______________________________________                                                                    STAGNANT                                          INLET           OUTLET      REGION, %                                         ______________________________________                                        1   ONE             ONE @ SIDE  65%                                           2   2 SYMMETRICAL   CENTER      60%                                           3   4 SYMMETRICAL   CENTER      50%                                           4   2, 40 degrees   ONE @ SIDE  40                                            5   BAFFLE          ONE @ SIDE  30                                            6   80% BAFFLE      ONE @ SIDE  8                                             ______________________________________                                    

2 symmetrical inlets means that there were two tangential inlets 180degrees apart from one another. In the case of 4 symmetrical inlets,they were spaced 90 degrees apart.

2 inlets spaced 40 degrees apart, with a single, central catalyst outletgave better results, but at a significant capital expense.

In simulation 5, with a baffle having the configuration similar to thatof FIG. 3, the active or non stagnant area of the catalyst bed wasdoubled, from 35% active to 70% active. This was accomplished with nomodifications to the spent catalyst inlet or the regenerated catalystoutlet. Surprisingly, a single spent catalyst inlet, with the baffle ofthe present invention, gave better results than splitting the catalystflow between two nozzles, and moving the catalyst sink to the center ofthe regenerator.

In simulation 6, the baffle design allows 20% of the catalyst from thecatalyst inlet to bypass the baffle, while 80% is baffled, i.e., splitinto two streams which are deflected or diverted roughly sideways. Thiscould be accomplished using the FIG. 4 design, or one of the otherdesigns could be modified by providing one or more holes or slits in thebaffle to allow 20% of the catalyst to "leak" through the baffle.

The approximate dimensions of a typical cross flow regenerator,associated with a typical 20,000 BPD cracking unit are as follows. Theoverall ID of the regenerator vessel is about 16 feet. The catalyst flowis 1200 tons/hr into the regenerator. The catalyst is added via onenormal inlet pipe having an ID of 18 inches. The catalyst velocity as itleaves the inlet is about 5 feet per second. It is discharged at anangle (40 degrees) as shown in FIG. 1 into a dense phase fluidized bedof catalyst having a depth of about 12 to 20 feet. The catalyst sink, orbathtub, has an ID of about 5 feet for withdrawal of catalyst. The sinkis at the opposite side of the regenerator from the catalyst inlet.

Many cross-flow regenerators are somewhat larger than this. Theregenerator associated with a 50-60,000 BPD unit will have a catalystinventory of around 200 tons and will be much larger than the smallerunit described above. The regenerator diameter will be about 30 to 36feet, and the catalyst inlet line will have an ID of about 3 feet. Thecatalyst velocity in the inlet line will still be about the same, e.g,about 6 fps. The catalyst flow in such a unit will be 3600 tons per hourinto the regenerator. The dense phase fluidized bed of catalyst willhave a depth of 10-15 feet. The catalyst sink or bathtub will have an IDof about 7 or 8 feet.

The conditions in the regenerator re. air flow, temperature, catalysttype, are all conventional. The invention has nothing to do with a newcatalyst, it is directed solely to reducing the stagnant regions inexisting cross-flow type regenerators to improve their operation.

BAFFLE DESIGN

The baffle should have a width equal to 100 to 400% of the width of thecatalyst inlet. The baffle should extend from the base of the dense bed,i.e., from the top of the air grid, to the base of the catalyst inletline, and preferably to the top of the catalyst inlet line, and mostpreferably to the top of the catalyst dense bed.

The baffle preferably is placed normal to the flow of incoming catalyst,but satisfactory operation may be achieved with a generally verticalbaffle.

The baffle may be a flat plate, but preferably is bent or curved toconform to the walls of the catalyst regenerator. Other shapes, such asa plow, hemisphere, cone, and the like may be used, but not necessarilywith equivalent results. The essential feature of a satisfactory baffleis that it will divert a majority of the incoming catalyst to one or theother side of the cross flow type regenerator. Splitting catalyst flowin two, and diverting catalyst at right angles from the direction offlow into the cross flow regenerator is preferred, but some lesserdiversion, e.g., diverting catalyst only 45 to 85 degrees from thedirection of catalyst flow into the regenerator will still bring about aconsiderable improvement in regenerator operation. Use of a poorlysealed baffle, that allows some flow of catalyst over or under thebaffle will not seriously impair operation, so long as a majority of theincoming catalyst is diverted sideways. Use of a poorly sealed baffle,or a baffle with holes or slots cut in, or two baffles which arerelatively close together, with a relatively small opening in between,may actually improve operation some, in reducing the stagnant area onthe other side of the baffle, across from the catalyst inlet. This finetuning of baffle design is beneficial, but may require an inordinateamount of site specific testing. Testing of the baffle shape in aregenerator model, or testing in a computer simulator, may be used toconfirm if a desired baffle shape and size will give satisfactoryresults. Usually the cost of exotic shapes will not be justified by theresults achieved in use, and the concerns over having a baffle whichwill operate without failure for at least a year and preferably for twoor three years make clean, simple baffle designs preferable.

We found that even further improvements could be made by using animperfect baffle. Our computer simulation shows that when we use abaffle which allows significant amounts of the catalyst flow to "leak"or pass through the baffle, the stagnant zone behind the baffle isgreatly reduced, and can even be eliminated. This allows the residualstagnant regions to be greatly reduced or eliminated. A baffle whichallows 20% of the catalyst inlet to pass through the baffle reduces thestagnant region of the dense phase bubbling bed to less than 10%.Although this is a significant improvement, the use of a perforatedbaffle, or a baffle with a large hole in the center, or one which istilted or notched so that it allows 10-30% of the catalyst to passunbaffled, introduces concerns about mechanical reliability. Rather thanuse the best design, in regards to reducing stagnant regions, it may bebetter overall to use a design which is simpler, and will last longer.

The baffle will give better results when it is radially displaced fromthe catalyst inlet The optimum spacing depends somewhat on baffle sizeand shape, and somewhat on the velocity of the spent catalyst enteringthe regenerator. For a regenerator of 16 feet diameter, with a 16 footdeep dense phase fluidized bed, the optimum spacing of the baffle fromthe regenerator wall 2 is about two feet, when the velocity of catalystin the spent catalyst transfer line 4 is about 5 feet/second. When thecatalyst velocity is higher, it is better to provide a greater distancebetween the baffle and the wall of the regenerator. For a 10 fps spentcatalyst velocity, and this is believed to be about the highest velocitythat would normally be encountered, a spacing of about 3 feet from thewall would give better results. The optimum shape of the baffle ineither case, whether 2' or 3' from the wall, would be a curved, verticalwall defining part of a circle having as its center the center of theregenerator.

Expressed in more generalized terms, the baffle should have a widthequal to 1 to 4 times the width of the catalyst inlet, preferably from1.5 to 3 times the width of the catalyst inlet, and most preferably from1.75 to 2.5 times the width of the catalyst inlet.

The baffle should be spaced from the catalyst inlet by a distance equalto 0.75 to 5 times the width of the catalyst inlet, preferably from 0.8to 4 times the width of the catalyst inlet, and most preferably from 1to 2 times the width of the catalyst inlet.

The baffle should be parallel to, or curved slightly inward from, thewalls of the catalyst regenerator 2.

Rather than attach and anchor the baffle to the air grid or some otherpart of the base of the regenerator vessel, it is also possible toattach the baffle to the coked catalyst inlet, or to the wall of theregenerator. In a preferred embodiment, the baffle comprises a cone,wedge or plow shaped "hat" which is attached to an extension of thecatalyst inlet, or attached to the wall of the regenerator vessel nearto the catalyst inlet. FIGS. 4 shows a wedge shaped "hat", somethinglike a "coolie hat". This design can achieve bypassing, if desired, byallowing catalyst to overflow or underflow the baffle, or the hat maycontain a relatively simple, elliptical or circular opening. The wedgeportions split the incoming catalyst flow into two streams which arediverted to the right and left sides of the catalyst inlet stream. Theopening allows a desired portion to bypass the baffle, and reduce oreliminate the stagnant area that would be created by a large bafflesealed to the regenerator air grid.

Other mechanical means may also be used to split the catalyst flow atleast into two streams after admission of the coked catalyst to theregenerator. A long catalyst inlet line extending well into theregenerator, with a plugged end and slit sides, can functionallyaccomplish the same thing as the preferred baffle arrangement.Conventional fluidic control devices can be used to split and directcoked catalyst. High pressure streams of air or inert gas can be used tosplit incoming catalyst flow. Mechanical driven stirrers or paddles canbe used to divert slugs of coked catalyst alternatively from one side ofthe regenerator vessel to the other side. The cost and complexity ofsuch mechanical approaches, and the need for the baffle to survive foryears in an environment that resembles a sandblasting machine more thananything else, will usually make the simple approaches better inpractice.

The process and apparatus of the present invention will improve catalystflow in the dense bed of a cross-flow type regenerator and increase thecarbon burning capacity of the regenerator, allowing the regenerator toproduce catalyst with lower residual carbon levels, or alternatively toincrease catalyst throughputs. The better operation of the dense bedwill greatly simplify the design and operation of the air grid used toadd combustion air. Because of more uniform bed operation, and moreefficient use of combustion air, there will be a reduction in COemissions, and a reduction in NOx emissions that would otherwise beassociated with localized high concentrations of air due to stagnantregions in the prior art design.

We claim:
 1. A cross-flow FCC catalyst regeneration apparatus for thefluidized catalytic cracking of hydrocarbons by contact with a source ofregenerated fluidized catalytic cracking (FCC) catalyst to producecatalytically cracked products and spent catalyst, and for theregeneration of coked FCC catalyst, comprising:a regenerator vesseldefined by a cylindrical sidewall and a diameter of at least 8 feet formaintaining a dense phase, bubbling fluidized bed of catalyst having adepth of at least 8 feet; a single catalyst inlet and a single catalystoutlet, wherein said catalyst inlet is defined by a downwardly connectedcoked FCC catalyst inlet normal to the sidewall having an inlet diameterof at least 1 foot and connective with the sidewall of said regeneratorfor discharging coked catalyst downward at a 40 degree angle into saidregenerator vessel; a regeneration gas inlet connective with an airdistribution means in a lower portion of said regenerator vessel; a fluegas outlet means in an upper portion of said regenerator vessel forremoval of flue gas; said catalyst outlet consisting essentially of asingle non-centrally located regenerated catalyst outlet located in alower portion of said baffled regenerator vessel at the opposite side ofthe regenerator vessel from the catalyst inlet; a baffle comprising amatched pair of rectangular plates symmetrically connected at an edgethereof to form an angle of 90 to 150 degrees, and wherein said baffleis inclined at an angle from about 10 to 75 degrees to horizontal andspaced inwardly inside said vessel from said catalyst inlet by adistance at least equal to 50% of the diameter of said coked catalystinlet and having a baffle width, as measured on a plane normal to saidcoked catalyst at least equal to the diameter of said coked catalystinlet and wherein said baffle has a surface area and contains holes orslits equal to 10-30% of the baffle area.
 2. A cross-flow FCC catalystregeneration apparatus for the fluidized catalytic cracking ofhydrocarbons by contact with a source of regenerated fluidized catalyticcracking (FCC) catalyst to produce catalytically cracked products andspent catalyst, and for the regeneration of coked FCC catalyst,comprising:a regenerator vessel defined by a cylindrical sidewall with adiameter of at least 8 feet for maintaining a dense phase, bubblingfluidized bed of catalyst having a depth of at least 8 feet; a singlecatalyst inlet and a single catalyst outlet, wherein said catalyst inletis defined by a downwardly connected coked FCC catalyst inlet normal tothe sidewall, having an inlet diameter of at least 1 foot and connectivewith the sidewall of said regenerator for discharging coked catalystinto said regenerator vessel; a regeneration gas inlet connective withan air distribution means in a lower portion of said regenerator vessel;a flue gas outlet means in an upper portion of said regenerator vesselfor removal of flue gas; said catalyst outlet consisting essentially ofa single non-centrally located regenerated catalyst outlet located in alower portion of said regenerator vessel at the opposite side of theregenerator vessel from the catalyst inlet; a baffle having a bafflearea disposed normal to the coked catalyst inlet, and spaced inwardlyinside said vessel from said catalyst inlet by a distance at least equalto 50% of the diameter of said coked catalyst inlet and having a bafflewidth, as measured on a plane normal to said coked catalyst inlet, atleast equal to the diameter of said coked catalyst inlet and containingholes or slits equal to 10-30% of the baffle area.